Contemporary selective call systems, e.g., paging systems, employ messaging schemes that can typically deliver voice, numeric, or alphanumeric messages to subscribers. Recently, Motorola's FLEX.TM. protocol is becoming accepted as a world-wide standard protocol for selective call communication. Additionally, Motorola provides a ReFleX.TM. protocol that allows selective call systems to handle two-way communication, e.g., acknowledge-back (Ack-Back) messaging, with portable transceivers, such as the Motorola Personal Messaging Unit (PMU) named Tango.RTM.. In a ReFlex.TM. communication system, a central system can send wireless messages to a portable transceiver unit such as a PMU, and the PMU can send both scheduled and unscheduled wireless messages to the central system.
A two-way communication system such as Motorola's ReFlex.TM. communication system, allows a central system to verify that a portable transceiver unit (portable unit) received a wireless message transmitted by the central system to the portable unit. A confirmation message, e.g., an Ack-Back response message, sent from the portable unit back to the central system in response to having received a wireless message therefrom provides an affirmative confirmation back to the central system that the wireless message was reliably delivered and received by the portable unit. This handshake messaging, i.e., sending a confirmation response message back to a central system for each wireless message received by a portable unit, can significantly enhance the reliability of communication in a selective call system. However, the increased number of transmitted messages due to the handshake messaging increases the message communication and message processing time delays in the selective call system. This added delay tends to reduce the message communication efficiency of the selective call system, which may not be acceptable under certain operational conditions of the selective call system, as will be discussed below.
Under certain operational conditions in the selective call system, for example, messaging traffic may be high for an available message communication throughput capacity for the selective call system. Any significant additional message traffic can detrimentally affect the operational efficiency of system resources, such as limited by a messaging throughput capacity of a wireless communication channel, or limited by messaging throughput capacity of communication links, or limited by an operational efficiency of central system resources such as near-full memory queues or overloading of tasks for devices that handle messaging operations, or a combination of all of the above communication phenomena.
Generally, the number of messages that a selective call system can handle during peak communication traffic periods constrains the number of total customers that can be serviced by the selective call system. The total number of customers handled by the selective call system typically determines the commercial viability of the selective call system.
Furthermore, although conventional Ack-Back messaging can maintain a high level of reliability in message communication by sending an immediate Ack-Back message in response to every wireless message received by a portable unit, under certain messaging conditions transmitting an immediate Ack-Back message response for every wireless message received by a portable unit may not be commercially practicable.
Specifically, to enhance the likelihood of commercial viability of a selective call system the messaging throughput capacity of the selective call system should be as high as possible. Normally, a selective call system has a one-way messaging throughput capacity that is constrained by the maximum number of wireless messages that the central system can transmit to the portable units over a unit of time. The selective call system also has a two-way messaging throughput capacity that is constrained by the maximum number of wireless messages that the central system can transmit to portable units while the portable units send Ack-Back messages back to the central system in response to receiving the wireless messages therefrom over a unit of time. For a particular selective call system, the one-way messaging throughput capacity is normally higher than the two-way messaging throughput capacity. Therefore, to enhance the likelihood of commercial viability of a selective call system the messaging throughput capacity of the selective call system should be as high as possible, preferably approaching the one-way messaging throughput capacity that is higher than the two-way messaging throughput capacity.
As an example, under high communication traffic conditions the selective call system's total messaging throughput capacity can be significantly constrained by the messaging throughput capacity consumed by the portable units sending Ack-Back response messages to the central system. The additional communication traffic and processing time delays due to the Ack-Back response messages may reduce the total number of wireless messages that can be delivered by the selective call system during the high communication traffic conditions.
Furthermore, acknowledgement messages as currently delivered in two-way messaging systems are unduly lengthy for the information they are conveying. Additionally, in current two-way synchronous paging protocols, all messages need to be scheduled on the reverse or inbound channel, even "unscheduled information" initiated by a user. The scheduling of "unscheduled information" creates additional traffic on both inbound and outbound channels that effectively reduced channel capacity.
Thus, what is needed is a method and apparatus in an acknowledge-back selective call system for providing the efficient use of the reverse channel that will take advantage of the minimal information required in acknowledgements and further reduce the inefficiencies involved with unscheduled information.